This invention relates to a method for producing a color filter and more particularly to a method for producing a color filter convenient to be employed as a color liquid crystal display device.
Up to now, color filters in general have been produced by a dyeing method, a printing method or a pigment dispersion method, in which a transparent substrate is colored using a binder containing a dye or a pigment.
However, since the dyeing method is a method for selectively dyeing a thin resin film on a substrate with a dyestuff, it is necessary to carry out the resist printing process and the photolithographic process each time the color is changed, such that the process becomes complex with consequent rise in production costs. On the other hand, since the dyestuff is employed as a coloring agent, the product is poor in thermal resistance, weatherability or resistance against chemicals. Although there is no necessity of carrying out the resist printing process with the above printing method, there is a limitation imposed on refinement of color patterns, such that the more variegated in the color pattern, the precision of printing position becomes the worse. Although it is possible to generate fine patterns with the pigment dispersion method, the photolithographic process of high precision needs to be carried out each time the color is changed, thus complicating the process.
On the other hand, there has been proposed a method for producing a color filter by an electrodeposition coating method. For example, with the electrodeposition method for preparation of the color filter, since a transparent filter is previously formed with a pre-set pattern and placed in a vat containing an ionized high molecular material containing a dye or a pigment dissolved or dispersed in a solvent for producing the color filter under application of an electrical voltage, a transparent electrode for the formation of the color filter is required in addition to the transparent display electrode. Since the transparent electrode needs to be insulated from one color to another, an etching process is required, while there is a risk of the decreased yield due to line defects produced by electrical shorting. Besides, since respective pixels need to be electrically coupled to one another, there is imposed a limitation on pixel arraying.
In the Japanese Laid-open Patent Applications Nos. 61-203403 (1986), 61-272720 (1986) and 61-279803 (1986), there is disclosed a method comprising coating a positive photosensitive composition on a glass substrate carrying a transparent electrode thereon, exposing and developing a preset color filter-forming portion, exposing an electrode surface, forming a color filter on the exposed transparent electrode surface by an electrodeposition method, exposing the entire assembly for removing the positive photosensitive composition and etching off the exposed transparent electrically conductive layer.
In the Japanese Laid-open Patent Application No. 63-249107, there is disclosed a method for forming a color filter by a high molecular electrodeposition method comprising forming a resist pattern having a window by photoetching.
In the Japanese Laid-open Patent Application No. 61-272720, there is disclosed a method comprising the steps of forming an electrically conductive layer on a substrate, forming a positive photosensitive coating film thereon, exposing the coating film and developing and removing the exposed portion with the above steps being repeated a number of times equal to the number of colors. Since the positive photosensitive coating film is employed, and only the exposed portion is solubilized in the developing solution, exposure and development operations can be repeated without exfoliating the photosensitive coating film. Although the positive photosensitive coating film need not be exfoliated and can be re-used with this method, it is necessary to carry out the steps of light exposure, development and coloring a number of times equal to the number of colors. With the currently used color filter, not only red, green and blue colors, but also a black matrix and a transparent outer frame are required, so that the number of repetition of the above steps is correspondingly increased. Especially, with the above method, the number of steps of electrodeposition followed by exposure equal to the number of colors less one is required. However, since the light exposure device is complicated, the step of electrodeposition followed by light exposure needs to be carried out with meticulous attention and painstaking operations of washing and drying after the electrodeposition, thereby complicating the process. In addition, the step of introducing and removing the substrate into and out of the light exposure device poses a significant work load. The color filter needs to be formed without exfoliating the photosensitive film even once, while the steps of electrodeposition and heating for drying need to be carried out a large number of times thereby affecting photosensitivity and solubility of the photosensitive coating film. The result is that portions which should be removed at the time of resist removal cannot be removed completely and are left over, thus producing significant production problems. In addition, if the production line is taken into consideration, it is necessary to provide a number of expensive light exposure devices equal to the number of times of the exposure operations for repetition of the steps comprising electrodeposition and subsequent exposure. Thus, there is raised a demand for reducing the number of times of introducing and removing the substrate and especially for minimizing the number of processes of introducing the substrate into the exposure device after the coloring step.